libgloss: Do not apply non-existent patch

When newlib and libgloss were updated to 4.3.0, SRC_URI was updated to
append a fix-rs6000-cflags.patch file when building on PowerPC, but this
file was not added to the repo.

Remove appending the missing patch.

Signed-off-by: Robert Joslyn <robert.joslyn@redrectangle.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>