octeontx2-pf: fix "UBSAN: shift-out-of-bounds error"

octeontx2-pf: fix "UBSAN: shift-out-of-bounds error"

[ Upstream commit 85f4b0c650d9f9db10bda8d3acfa1af83bf78cf7 ]

This patch ensures that the RX ring size (rx_pending) is not
set below the permitted length. This avoids UBSAN
shift-out-of-bounds errors when users passes small or zero
ring sizes via ethtool -G.

Fixes: d45d8979840d ("octeontx2-pf: Add basic ethtool support")
Signed-off-by: Anshumali Gaur <agaur@marvell.com>
Link: https://patch.msgid.link/20251219062226.524844-1-agaur@marvell.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>