Fix loops in the SAM banzai() reset function

(Note: I have only compile-tested this code. I haven't got a Due to actually test this, nor the know-how to tell if the fixed code is really correct, but I am sure that the old code is wrong).

The code used to say:

  while (EFC0->EEFC_FSR & EEFC_FSR_FRDY == 0);

This triggered a compiler warning, which is why I looked at this line
more closely:

	warning: suggest parentheses around comparison in operand of '&'

As the warning indicates, because the == operator has higher precedence
than the & operator, the compiler is interpreting this line as:

  while (EFC0->EEFC_FSR & (EEFC_FSR_FRDY == 0));

Since EEFC_FSR_FRDY is defined as 1, (EEFC_FSR_FRDY == 0) is always
false (== 0) and this reduces to:

  while (EFC0->EEFC_FSR & 0);

Which reduces to:

  while (0);

So effectively this line is a no-op.

This commit adds parenthesis to restore the intended behaviour.