octeontx2-af: fix array bound error

This patch fixes below error by using proper data type.

drivers/net/ethernet/marvell/octeontx2/af/rpm.c: In function
'rpm_cfg_pfc_quanta_thresh':
include/linux/find.h:40:23: error: array subscript 'long unsigned
int[0]' is partly outside array bounds of 'u16[1]' {aka 'short unsigned
int[1]'} [-Werror=array-bounds]
   40 |                 val = *addr & GENMASK(size - 1, offset);

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Link: https://lore.kernel.org/r/20220211155539.13931-1-hkelam@marvell.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>