samd: SPI: improve conditional code

I recently misdiagnosed a "maybe-uninitialized" diagnostic as a bug in
asf4.  However, the problem was in our SPI code.

A special case for samr21 MCUs was being applied to same54p20a and possibly
other D5x/E5x MCUs, since the check was simply for pin PC19 existing at all.

Change the check to use the macro PIN_PC19F_SERCOM4_PAD0 which is only
defined if special function F of pin PC19 is SERCOM4 PAD0.

Reorganize the code a little bit so that brace-matching in editors is
not confused by the conditionalized code, including an unrelated change
for APA102_SCK's condition.

Revert the change to the Makefile that incorrectly attempted to silence
the diagnostic.

0 files changed, 0 insertions, 0 deletions