LoongArch: Simplify "BGT foo, zero" with BGTZ

Support for the syntactic sugar is present in upstream binutils port
from the beginning. Use it for shorter lines and better consistency.
Generated code should be identical.
Signed-off-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/lib/clear_user.S

@@ -32,7 +32,7 @@ SYM_FUNC_START(__clear_user)
 1:	st.b	zero, a0, 0
 	addi.d	a0, a0, 1
 	addi.d	a1, a1, -1
-	bgt	a1, zero, 1b
+	bgtz	a1, 1b
 
 2:	move	a0, a1
 	jr	ra

arch/loongarch/lib/copy_user.S

@@ -35,7 +35,7 @@ SYM_FUNC_START(__copy_user)
 	addi.d	a0, a0, 1
 	addi.d	a1, a1, 1
 	addi.d	a2, a2, -1
-	bgt	a2, zero, 1b
+	bgtz	a2, 1b
 
 3:	move	a0, a2
 	jr	ra