MAINTAINERS: Fix file entry for MAX77693 DT

Commit b38213c6 ("dt-bindings: mfd: maxim,max77693: Convert to
dtschema") converts max77693.txt to maxim,max77693.yaml and adjusts the
file entry in MAINTAINERS accordingly.

Unfortunately, the merge commit afb67df3 ("Merge branches [...] into
ibs-for-mfd-merged") resolves some conflict in MAINTAINERS in such a way
that the file entry for the converted text file max77693.txt, removed in
the commit above, is added back into MAINTAINERS.

Remove the file entry to this converted text file in MAXIM PMIC AND MUIC
DRIVERS FOR EXYNOS BASED BOARDS.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220601073511.15721-1-lukas.bulwahn@gmail.com