usb: host: oxu210hp-hcd: Replace fake flex-array with flexible-array member

Zero-length arrays as fake flexible arrays are deprecated and we are
moving towards adopting C99 flexible-array members instead.

Transform zero-length array into flexible-array member in struct
ehci_regs.

Address the following warnings found with GCC-13 and
-fstrict-flex-arrays=3 enabled:
drivers/usb/host/oxu210hp-hcd.c:3983:30: warning: array subscript i is outside array bounds of ‘u32[0]’ {aka ‘unsigned int[]’} [-Warray-bounds=]
drivers/usb/host/oxu210hp-hcd.c:3986:38: warning: array subscript i is outside array bounds of ‘u32[0]’ {aka ‘unsigned int[]’} [-Warray-bounds=]
drivers/usb/host/oxu210hp-hcd.c:3971:30: warning: array subscript i is outside array bounds of ‘u32[0]’ {aka ‘unsigned int[]’} [-Warray-bounds=]
drivers/usb/host/oxu210hp-hcd.c:3978:30: warning: array subscript i is outside array bounds of ‘u32[0]’ {aka ‘unsigned int[]’} [-Warray-bounds=]
drivers/usb/host/oxu210hp-hcd.c:3523:30: warning: array subscript i is outside array bounds of ‘u32[0]’ {aka ‘unsigned int[]’} [-Warray-bounds=]
drivers/usb/host/oxu210hp-hcd.c:2774:39: warning: array subscript port is outside array bounds of ‘u32[0]’ {aka ‘unsigned int[]’} [-Warray-bounds=]
drivers/usb/host/oxu210hp-hcd.c:3569:35: warning: array subscript <unknown> is outside array bounds of ‘u32[0]’ {aka ‘unsigned int[]’} [-Warray-bounds=]
drivers/usb/host/oxu210hp-hcd.c:3888:36: warning: array subscript port is outside array bounds of ‘u32[0]’ {aka ‘unsigned int[]’} [-Warray-bounds=]
drivers/usb/host/oxu210hp-hcd.c:2911:45: warning: array subscript i is outside array bounds of ‘u32[0]’ {aka ‘unsigned int[]’} [-Warray-bounds=]

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
routines on memcpy() and help us make progress towards globally
enabling -fstrict-flex-arrays=3 [1].

Link: https://github.com/KSPP/linux/issues/21
Link: https://github.com/KSPP/linux/issues/259
Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/Y/gynI9Wv8RZTD8M@workSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/oxu210hp-hcd.c

@@ -169,7 +169,7 @@ struct ehci_regs {
 #define FLAG_CF		(1<<0)		/* true: we'll support "high speed" */
 
 	/* PORTSC: offset 0x44 */
-	u32		port_status[0];	/* up to N_PORTS */
+	u32		port_status[];	/* up to N_PORTS */
 /* 31:23 reserved */
 #define PORT_WKOC_E	(1<<22)		/* wake on overcurrent (enable) */
 #define PORT_WKDISC_E	(1<<21)		/* wake on disconnect (enable) */