mfd: lm3533: Fix unused variable build warning

We were getting build warning about unused variable 'ret'.
The commit c749db571dcf has removed the use of ret but missed removing
the variable which is unused now.

Fixes: c749db571dcf ("mfd: lm3533: Simplify function return logic")
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>