drm/tinydrm: make function st7586_pipe_enable static

drm/tinydrm: make function st7586_pipe_enable static

The function st7586_pipe_enable  is local to the source
and does not need to be in global scope, so make it static.

Cleans up sparse warning:
symbol 'st7586_pipe_enable' was not declared. Should it be static?

Signed-off-by: Colin Ian King <[email protected]>
Acked-By: David Lechner <[email protected]>
[noralf: fixed: Alignment should match open parenthesis]
Signed-off-by: Noralf Trønnes <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]