x86/boot/compressed/64: Remove unused variable

Fix gcc warning:

arch/x86/boot/compressed/pgtable_64.c: In function 'find_trampoline_placement':
arch/x86/boot/compressed/pgtable_64.c:43:16: warning: unused variable 'trampoline_start' [-Wunused-variable]
unsigned long trampoline_start;
^

Signed-off-by: Zhenzhong Duan <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Acked-by: Kirill A. Shutemov <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/x86/boot/compressed/pgtable_64.c

···
 static unsigned long find_trampoline_placement(void)
 {
 	unsigned long bios_start = 0, ebda_start = 0;
-	unsigned long trampoline_start;
 	struct boot_e820_entry *entry;
 	char *signature;
 	int i;