mfd: cs42l43: Sanity check firmware size

mfd: cs42l43: Sanity check firmware size

Currently the code checks if a firmware was received, however it does
not verify that the firmware size is larger than the firmware header. As
the firmware pointer is dereferenced as a pointer to the header
structure this could lead to an out of bounds memory access. Add the
missing check.

Fixes: ace6d1448138 ("mfd: cs42l43: Add support for cs42l43 core driver")
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://patch.msgid.link/20260508134804.1787461-1-ckeepax@opensource.cirrus.com
Signed-off-by: Lee Jones <lee@kernel.org>