mesa: do not use format string as literal string

mesa: do not use format string as literal string

This fixes a couple of  errors when building in Android:

external/mesa3d/src/mesa/main/shaderapi.c:293:49: error: format string
is not a string literal (potentially insecure)
[-Werror,-Wformat-security]
         _mesa_error(ctx, GL_INVALID_OPERATION, caller);
                                                ^~~~~~
external/mesa3d/src/mesa/main/shaderapi.c:293:49: note: treat the string
as an argument to avoid this
         _mesa_error(ctx, GL_INVALID_OPERATION, caller);
                                                ^
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>