xhci: Use ilog2() rather than __ffs() for calculating SEGMENT_SHIFT

Use ilog2() rather than __ffs() for calculating SEGMENT_SHIFT as ilog2() can
be worked out at compile time, whereas __ffs() must be calculated at runtime.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Sarah Sharp <sarah.a.sharp@linux.intel.com>
cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
cc: linux-usb@vger.kernel.org
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>

drivers/usb/host/xhci.h

@@ -1239,7 +1239,7 @@ union xhci_trb {
 /* Allow two commands + a link TRB, along with any reserved command TRBs */
 #define MAX_RSVD_CMD_TRBS	(TRBS_PER_SEGMENT - 3)
 #define SEGMENT_SIZE		(TRBS_PER_SEGMENT*16)
-#define SEGMENT_SHIFT		(__ffs(SEGMENT_SIZE))
+#define SEGMENT_SHIFT		(ilog2(SEGMENT_SIZE))
 /* TRB buffer pointers can't cross 64KB boundaries */
 #define TRB_MAX_BUFF_SHIFT		16
 #define TRB_MAX_BUFF_SIZE	(1 << TRB_MAX_BUFF_SHIFT)