fix whitespace, no semantical changes

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
x32b2_rcpx() converts a 2bit into a sequence specific number (rcpx)
that has the same high bits when called with dna template 2bit as
when called with its reverse complement 2bit. x32b2_rcpx() is
self-reversible. When called with a rcpx it returns the original 2bit.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>