Macro rename and compiler error fix

[sebastian-carpenter]

WOLFSSL_RSA_PSS_ENCODING macro is not used in wolfSSL but is prefaced with WOLFSSL instead of WP.

Fixed test case for my compiler as well by updating array length to 6.
associated error:

test/test_tls1_prf.c: In function ‘test_tls1_prf_calc’:
test/test_tls1_prf.c:31:30: error: initializer-string for array of ‘unsigned char’ truncates NUL terminator but destination lacks ‘nonstring’ attribute (6 chars into 5 available) [-Werror=unterminated-string-initialization]
   31 |     unsigned char label[5] = "Label";
      |                              ^~~~~~~

compiler version: gcc (GCC) 15.1.1 20250521 (Red Hat 15.1.1-2)

[padelsbach]

LGTM