sparc64: remove cast from output constraints in math asm statements

The following asm statements generated a sparse warning:

        asm("addcc \n\t" : "=r" (((USItype)(r2)))

warning: asm output is not an lvalue

When asking on the sparse mailing list Linus replyed:

"
Those casts to (USItype) are all pointless to begin with (since the
values are of that type already!) and they mean that the expression
isn't something you can assign to (lvalue).
"

In the math emulation code drop all casts in the output
parts of the asm statements.

This fixes a lot of "warning: asm output is not an lvalue" sparse
warnings in math_64.c.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>