staging/fbtft: Hush checkpatch.pl warning about unnecessary line continuations

Use a single string literal as the fmt argument passed to dev_err()
instead of multiple string literals split with an embedded backslash
character.

Signed-off-by: Alexander Kapshuk <alexander.kapshuk@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>