mtd: Fix comparison in map_word_andequal()

Commit 9e343e87 ("mtd: cfi: convert inline functions to macros")
changed map_word_andequal() into a macro, but also changed the right
hand side of the comparison from val3 to val2.  Change it back to use
val3 on the right hand side.

Thankfully this did not cause a regression because all callers
currently pass the same argument for val2 and val3.

Fixes: 9e343e87 ("mtd: cfi: convert inline functions to macros")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>