phy: ti: j721e-wiz: Add missing include linux/slab.h

When compiling with CONFIG_PHY_J721E_WIZ, Hulk Robot reported:

drivers/phy/ti/phy-j721e-wiz.c: In function ‘wiz_mux_clk_register’:
drivers/phy/ti/phy-j721e-wiz.c:659:17: error: implicit declaration of function ‘kzalloc’; did you mean ‘vzalloc’? [-Werror=implicit-function-declaration]
  659 |  parent_names = kzalloc((sizeof(char *) * num_parents), GFP_KERNEL);
      |                 ^~~~~~~
      |                 vzalloc
drivers/phy/ti/phy-j721e-wiz.c:659:15: warning: assignment to ‘const char **’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
  659 |  parent_names = kzalloc((sizeof(char *) * num_parents), GFP_KERNEL);
      |               ^
drivers/phy/ti/phy-j721e-wiz.c:697:2: error: implicit declaration of function ‘kfree’; did you mean ‘vfree’? [-Werror=implicit-function-declaration]
  697 |  kfree(parent_names);
      |  ^~~~~
      |  vfre

Fixes: 040cbe76 ("phy: ti: j721e-wiz: Model the internal clocks without device tree input")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Shixin Liu <liushixin2@huawei.com>
Link: https://lore.kernel.org/r/20210408012829.432938-1-liushixin2@huawei.comSigned-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/phy/ti/phy-j721e-wiz.c

@@ -8,6 +8,7 @@
 
 #include <dt-bindings/phy/phy.h>
 #include <dt-bindings/phy/phy-ti.h>
+#include <linux/slab.h>
 #include <linux/clk.h>
 #include <linux/clk-provider.h>
 #include <linux/gpio.h>