parisc: silence uninitialized variable warning in dbl_to_sgl_fcnvff()

Smatch warns that is_tiny can be used uninitialized:

arch/parisc/math-emu/fcnvff.c:297 dbl_to_sgl_fcnvff()
error: uninitialized symbol 'is_tiny'.

This code is very old so that suggests the bug doesn't have a huge affect in real life. But I've read the code and it seems like a reasonable warning. Either way it should be harmless to initialize it to false and silence the static checker warning.

index 76c063f7d17c..f9357d9d4cb1 100644
@@ -148,7 +148,7 @@ dbl_to_sgl_fcnvff(
         register int src_exponent, dest_exponent, dest_mantissa;
         register boolean inexact = FALSE, guardbit = FALSE, stickybit = FALSE;
 	register boolean lsb_odd = FALSE;
-	boolean is_tiny;
+	boolean is_tiny = FALSE;
 
 	Dbl_copyfromptr(srcptr,srcp1,srcp2);
         src_exponent = Dbl_exponent(srcp1);